Issue 55

S.S. Ali et alii, Frattura ed Integrità Strutturale, 55 (2021) 187-197; DOI: 10.3221/IGF-ESIS.55.14

the aggregates are smaller than water molecules, but when the water molecules collide with the surface, atoms would break and water penetrate to the holes. Moreover, one of the reasons is the presence of silica in the surface of the aggregate which make their surfaces hydrophilic. By modifying the surface of aggregates with nano-Zycosil, this material due to their nano-meter size, penetrated into the pores of the aggregate and provided the hydrophobic properties. When the water collided the surface of the modified aggregates, it remained on the surface of them. Figs. 7 c and d, are taken after water boiling test and indicate the amount of stripping for modified and unmodified aggregates with 1% nano-Zycosil, respectively. The amount of stripping in the unmodified ones is significantly much more than the modified aggregates [20]. Thermal analysis results Fig. 8 shows TGA diagrams for the capsule components. As it is illustrated in Fig. 8, the mass loss of rejuvenator, nano Zycosil and epoxy resin starts to fall down at 230°C, 190°C and 260 °C, respectively. As mentioned before, the asphalt mixture mixing temperatures was between 160 and 180 °C. This means the capsule can resist the asphalt mixture mixing temperature range. In addition, Fig. 8 also shows, the most affected material by temperature is the scoria porous sand which lost a lot of mass between 30 and 160°C. That is because of the presence of water in its pores. So, to avoid such mass loss it is required before encapsulation, the porous sand should be heated in order to evaporate the moisture in its pores.

Figure 8: TGA diagrams of encapsulated ingredients.

ITS and ITF tests results In Figs. 9 a and b, results of ITS and ITF tests are shown, respectively. In Figs. 9 the prefix “Treated” means the material is modified with nano-Zycosil. As it is displayed in Fig. 9, different types of samples including asphalt mixture without capsules, with capsules, with modified capsules, modified aggregate and with modification of both capsules and aggregates by nano-Zycosil were experimented. According to Fig. 9 a, it can be seen that the capsules reduce the stiffness of asphalt mixture and have some effect on the mechanical characteristics of the asphalt mixture. This could happen because some of the capsules broke during the mixing. Another reason could be the diffrences in the adhesion between them and the asphalt binder compare to the adhesion between the main aggregates and the asphalt binder. In addition, during the mixing process, some of the capsules would break which results in releasing the rejuvenators. So, the released rejuvenators would soften the asphalt binder. Moisture susceptibility of asphalt mixtures could be predicted by tensile strength ratio (TSR), wet/dry (conditioning/ unconditioned) ratio of ITS values [18]. In general, the higher the TSR, the more resistance mixture against moisture induced distresses such as stripping. As shown in Fig. 9 a, the mixtures modified with nano-Zycosil had lower susceptibility against wet condition due to having higher TSR values. Treated Capsule & Aggregate-mixtures had the highest moisture resistance while +Capsule-mixtures performed the worst among the others. As a result, modified capsules and aggregates with nano-Zycosil improved the moisture resistance of asphalt mixture significantly regarding TSR values.

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